Throughout history, games that revolved around kicking a ball have been played in many countries. In the medieval European period, the rules varied greatly from place to place.
Football is a team sport played between two teams of eleven players. The team that scores the most points wins the game. Each team has a playbook of dozens to hundreds of plays. Each play is designed to score a point or advance the ball at least ten yards. The game consists of two periods, each consisting of 45 minutes. During the first period, the receiving team is given the ball from the spot where the previous play started.
The receiving team must advance ten yards or more in four plays. The offense then gets a new set of four downs, giving the offense a chance to score. If the offense fails to score a point in this period, the game is turned over to the defense.
In the NFL, the short axis of the football was between 21-1/4 and 21-1/2 inches. The air capacity was set at 12.5 to 13.5 psi.
If the ball goes out of bounds or the offensive team misses a field goal, the ball is placed at the spot where the play began. If the offensive team misses another field goal, the ball is placed at the opponent’s 20-yard line. A kick from the opponent’s 20-yard line is called a punt.
A touchdown is scored when the offensive team kicks the ball through the goal posts. This is analogous to a two-point conversion in rugby.